In many cases, a hearing aid with two hearing devices (binaural hearing aid, so-called binaural supply) is necessary or expedient in order to adequately provide assistance to a patient with defective hearing. In such cases digitally programmable hearing systems are nowadays used almost exclusively, in other words hearing systems, the electroacoustic characteristics of which can or must be adjusted externally by way of a computer. The main advantage of (digitally) programmable hearing systems is that a plurality of electroacoustic parameters can be adjusted in order to compensate for the hearing loss in a more precise manner. These hearing devices can use analog signal processing (digitally programmable analog hearing systems) or digital signal processing (fully digital hearing systems). Fully digital hearing devices are hearing systems which convert the analog microphone signal into a digital signal. The digital signal is then processed according to the commands of the programmed software (algorithm) and to the circuitry integrated on the chip. The digital signals are then converted back into analog signals and forwarded to the receiver. The incoming signal is measured here at specific time intervals (signal scanning). The more frequent the signal scanning, the better the reproduction of the input signal. Digitization allows significantly more complex analyses and filterings in respect of an optimum speech/interference noise ratio than was possible with analog systems.
Adjusting facilities (generally by hearing device acousticians) are used for the so-called adjustment of hearing devices, in other words for the adjustment of the parameters thereof (e.g. filter coefficients) or for the programming thereof, said adjusting facilities regularly being embodied as special computers with a special user software running thereupon and exchanging data with the hearing devices, by way of cables or wirelessly, during the adjustment. With the adjustment of binaural (including both ears) hearing aids, a correct assignment of the two hearing devices (HA1, HA2) to the ears (RE) and/or (LE) of the wearer must take place prior to the adjustment, because otherwise the data would be incorrectly assigned to the devices during the adjustment. This assignment of both hearing devices (HA1, HA2) to the ears (RE) and/or (LE) of the wearer for the purpose of the adjustment is also referred to by the person skilled in the art as side definition.
Side definition does not present any problems if the adjusting facility is connected to the hearing device or the hearing devices by way of a cable, because a clear assignment of the ear sides (right and left) to the data is easily possible with the aid of the cable. If the data is transmitted wirelessly between the adjusting facility and the hearing device however, a side definition is less simple.